Decision-making tool for structural integrity assessment of buried water-transmission mains using a geomechanical approach

Abstract

Renewal of aged drinking water pipes, especially for large-diameter water-transmission buried pipelines, called feeders, is necessary to ensure sustained access to drinking water services with both high quality and high performance. Available data are valuable for predicting feeder failures, nevertheless gradual decline in the performance of these aged pipes is not always clear in practice. The study of the mechanical behavior of the soil-pipe system (called geomechanical approach), can provide interesting elements to evaluate and/or predict the integrity of this type of systems. The mechanisms of geomechanical behavior are however difficult to learn because the pipes are placed in an uncertain environment. Indeed, the interaction of the soil on the pipe has an important influence on its stress and strain distribution. Simplified models of the Winkler type (the soil is modeled by springs with a stiffness named coefficient of subgrade reaction) are generally used and can effectively represent the complexity of this interaction, although the soil stiffness is still uncertain due to its spatial variability. The numerical modeling of the soil-pipe system implies the adoption of different strategies and steps in order to accelerate and optimize the computation in an uncertain context that involves the execution of several simulations. The methodology proposed in this study intends to optimize the resources for maintenance and thus to set up an efficient risk management which leads to associate the diagnosis, the prognostic and the decision-making concerning the desired performances of drinking water pipes, especially for large-diameter water-transmission pipelines. This study consists of two parts. First, the numerical modeling of the soil-pipe system is performed by combining a one-dimensional model in the longitudinal direction of the pipe and a two-dimensional model of the pipe cross-section. This combination of models allows to consider the effects of internal pressure, surface loading and the longitudinal and transverse interaction of the soil-pipe system in order to obtain settlement profiles and mechanical stresses along the pipe. Uncertainties and soil variability are incorporated into the numerical model through random fields. The second part presents the application of the developed approach in a context of patrimonial management of a network of feeders. Criticality indicators are defined to evaluate the performance of the pipe (displacement, stress, joint opening), according to a reliability approach, with respect to limit states defined in connection with inspection, maintenance or renewal strategies of the pipelines.